Rational strategy for power doubling of monolithic multijunction III-V photovoltaics by accommodating attachable scattering waveguides

While waveguide-based light concentrators offer significant advantages, their application has not been considered an interesting option for assisting multijunction or other two-terminal tandem solar cells. In this study, we present a simple yet effective approach to enhancing the output power of transfer-printed multijunction InGaP/GaAs solar cells. By utilizing a simply combinable waveguide concentrator featuring a coplanar waveguide with BaSO4 Mie scattering elements, we enable the simultaneous absorption of directly illuminated solar flux and indirectly waveguided flux. The deployment of cells is optimized for front-surface photon collection in monofacial cells. Through systematic comparisons across various waveguide parameters, supported by both experimental and theoretical quantifications, we demonstrate a remarkable improvement in the maximum output power of a 26%-efficient cell, achieving an enhancement of ~93% with the integration of the optimal scattering waveguide. Additionally, a series of supplementary tests are conducted to explore the effective waveguide size, validate enhancements in arrayed cell module performance, and assess the drawbacks associated with rear illumination. These findings provide a comprehensive understanding of our proposed approach towards advancing multi-junction photovoltaics.


Fig. S1
Fig. S1 Epitaxial stacks of InGaP/GaAs solar cells.a, Schematic structure of releasable InGaP/GaAs solar cell stacks epitaxially grown on a GaAs growth wafer, along with specifications of each layer, including materials, doping concentrations, and thicknesses.b, Cross-sectional scanning electron microscope (SEM) images of epitaxial stacks.

Fig. S2
Fig. S2 Process flow of InGaP/GaAs solar cells.Schematic illustration of processing steps from epitaxial stacks on the growth wafer to a complete cell on a glass substrate.

Fig. S3
Fig. S3 White scattering behavior of BaSO4-PDMS scattering waveguide.a, Schematic illustration of dispersing BaSO4 particles into PDMS and the fabricated result.b,c, Lowmagnification (b) and high-magnification (c) SEM images of the BaSO4 particles.d-f, Top-view SEM images of BaSO4-PDMS scattering waveguide with fBaSO4s of 0.1 (d), 8.3 (e), and 15.4 wt% (f).g, Photograph of BaSO4-PDMS scattering waveguides without and with BSR at various fBaSO4s.

Fig. S4
Fig. S4 BaSO4 particle size distribution.Measured size distribution of BaSO4 particles using the dynamic light scattering system.The particles were dispersed in isopropyl alcohol.

Fig. S7
Fig. S7 Optical modeling of various scattering waveguide modules with a single InGaP/ GaAs solar cell.a,b, Calculated absorbed photon flux in emitter/base (Aflux,e/b) of each subcell for BSRless (a) and BSR-added (b) modules at various fBaSO4s.The light gray line indicates the AM 1.5G solar flux.c, Calculated J * S-Qs of top (J * S-Q,top) and bottom (J * S-Q,bot) subcells for modules corresponding to (a,b)

Fig. S9
Fig. S9 Temperature dependence of the InGaP/GaAs module performance with scattering waveguide.Measured Isc (a), Voc (b), FF (c), and Pmax (d) of the 15.4 wt% module normalized by their initial values (Isc,0, Voc,0, FF0, and Pmax,0 at 32.8 o C), respectively, as a function of the sample temperature.

Fig. S11
Fig. S11 Photon delivery calculation.a, Schematic illustrations of scattering waveguide modules for the photon delivery study.b,c, Calculated J * S-Qs of the BSR-less (b) and BSR-added (c) modules under the area-confined (0.5 × 15 mm 2 bar) AM 1.5G solar spectrum as a function of di, center-to-edge distance between cell and illumination aperture, at various fBaSO4s

Fig. S13
Fig. S13 Confinement effect calculation.a, Schematic illustration of the setup for spatially square-confined cell illumination (side length: ai) or BaSO4-PDMS scattering sublayer (side length: asw).b,c, Calculated current gain J * S-Q/J * S-Q,0 of the BSR-less (b) and BSR-added (c) modules as a function of ai or asw at various fBaSO4s.

Table . S1
3-dimensional ray-tracing simulation setup for calcuating the photon flux incident on the front cell surface.